I. Field of the Invention
The invention relates to mechanisms for achieving cuts in hard earth formations such as cuts achieved for ditching operations in conjunction with pipeline installation, especially where such earth formations take the form of rock, ice, permafrost, etc. More particularly, the invention relates to the positioning of the conical cutting bits on the chain link conveyor assembly of an earth cutting apparatus to facilitate even bit wear.
II. Description of the Prior Art
Mechanisms for achieving cuts in earth formations are well known and equally well known are mechanisms for achieving cuts in hard earth formations such as those typically involved when subterranean mining operations are being conducted, such as coal mining, where sedimentary rock is removed for exposure of veins of coal or other minerals. Similar earth cutting techniques are utilized in ditching operations preparatory to the installation of pipeline in the earth's surface.
A well known and commercially successful type of apparatus for cutting hard earth formations is the earth cutting machine described in U.S. Pat. No. 3,954,301 to Clarence L. Stepp of Houston, Tex. This patented machine includes a chain link conveyor assembly which is articulated from a prime mover vehicle. The outwardly facing portion of the chain links include a plurality of pointed conical bits, typically having tungsten carbide tips, which are staggered for cutting along differing cutting paths along the width of the conveyor. At least one bit is positioned on each side of the conveyor for cutting the gauge of the kerf. During earth cutting operations the depth of the cut or kerf is controlled by the angulation of the conveyor mechanism relative to the prime mover.
A severe problem associated with prior cutting operations utilizing the described apparatus is the uneven and rapid wearing of the conical bits. It has been found that the tip portion of some bits wear down exceptionally fast. Other bits have been found to wear along one side very rapidly until they are no longer usable. Other kinds of uneven and rapid wear conditions have been experienced.